This invention relates to a process for preparing electrically conductive fibrous material from a thermally stabilized acrylic fibrous material, and to the fibrous material produced thereby. The invention further relates to an electrically conductive composite comprising electrically conductive thermally stabilized acrylic fibrous material surrounded with a continuous polymeric or resinous matrix and to a process for preparing the same. The invention is useful for EMI (electromagnetic interference) shielding, and electrostatic discharge as well as in forming electrically conductive resins and paints.
It is known in the art to treat polyacrylonitrile fibers with cupric sulfate, hydroxylamine, and thiosulfate to produce electrically conductive fibers having adsorbed thereto copper sulfide in the forms of digenite, chalcocite, and covellite, alone or in conjunction with sulfides of noble metals, in a total amount of up to 30 percent in terms of elemental copper based on the weight of the starting fiber. (See Tomibe et al, European Pat. No. 0 086 072 and U.S. Pat. No. 4,336,028.) However, these fibers possess various deficiencies: the polyacrylonitrile fibers are relatively heat unstable and tend to lose their integrity in various applications; for example, if the fibers are contacted with molten resinous material, the fibers disintegrate. Further, the copper sulfide content is only partially in the form of covellite, the most conductive of the forms of copper sulfide, thus rendering the fibers inadequately conductive for many applications. Additionally, high levels of copper sulfide incorporation (e.g., greater than about 30 weight percent) are not possible according to the processes of the prior art.
It is also known to produce copper sulfide-coated electrically conductive fibers from other synthetic or natural polymers. (See Tomibe et al, U.S. Pat. Nos. 4,364,739, 4,378,226, and 4,410,593.) However, each of these fibers possesses the same deficiencies as the above-described fibers.
It is also known to produce elemental copper-plated acrylate/styrene/acrylonitrile articles or articles of other polymers by depositing a copper compound and subsequently reducing with a borohydride. (See U.S. Pat. Nos. 4,234,628 and 4,246,320 to DuRose and Coll-Palagos et al, respectively.) However, many of the above-noted deficiencies are inherent in these articles.
Further, it is known in the art to produce composite articles by loading organic fibrous material and/or inorganic fillers into a resinous matrix. For example, U.S. Pat. No. 2,956,039 to Novak et al discloses metal-plated fibers (e.g., of wool, polyethylene terephthalate, or nylon) or metal particles in admixture with an epoxy resin to produce an electrically insulating composition. U.S. Pat. No. 3,658,750 to Tsukui et al discloses an electrically insulating composition comprising a thermosetting resin and 40 to 80 volume percent of a powdered filler which may be cuprous sulfide or cupric sulfide. U.S. Pat. No. 4,155,896 to Rennier et al discloses a composition comprising copper plated steel or glass fibers dispersed in an organic coating. U.S. Pat. No. 3,658,748 to Andersen et al discloses a composite comprising reinforcing fibers (e.g., of polyacrylonitrile) embedded in a thermosettable resin. However, each of these compositions possesses various deficiencies, including insufficient conductivity for certain applications and difficulty of processing the composite due to poor thermal stability of the filler material.
It is therefore an object of the present invention to provide a process for preparing improved electrically conductive fibrous materials, particularly highly conductive materials.
It is a still further object of the present invention to provide a process for preparing an improved electrically conductive fibrous material which is flexible and ductile.
It is a further object of the present invention to provide an improved electrically conductive fibrous material having covellite copper sulfide in association therewith, wherein the copper sulfide is substantially entirely in the form of covellite copper sulfide.
It is a still further object of the invention to provide a process for preparing a composite article which incorporates an improved electrically conductive fibrous material which is heat stable and which may be processed in a molten polymeric matrix without destruction of the fibrous material.
It is a still further object of the invention to provide an electrically conductive monolithic composite incorporating an improved electrically conductive fibrous material.
It is a still further object of the invention to provide an electrically conductive polymer composition incorporating an improved electrically conductive fibrous material.
It is a still further object of the invention to produce fibrous material which is suitable for use in electrostatic discharge and EMI shielding applications and other applications where electrically conductive composites are desired.
These and other objects, as well as the scope, nature, and utilization of the claimed invention will be apparent to those skilled in the art by the following detailed description and appended claims.
SUMMARY OF THE INVENTION
According to the present invention, an electrically conductive fibrous material is prepared from a thermally stabilized acrylic fibrous material by
(a) supplying a source of cuprous ions to the thermally stabilized acrylic fibrous material to produce a cuprous ion-impregnated thermally stabilized acrylic fibrous material;
(b) contacting the resulting cuprous ion-impregnated thermally stabilized acrylic fibrous material with a sulfiding agent capable of sulfiding the cuprous ions to form covellite copper sulfide in association with the thermally stablized acrylic fibrous material; and, optionally,
(c) washing the resulting thermally stabilized acrylic fibrous material containing associated covellite copper sulfide to remove residual reactants adhering to the same.
In a preferred embodiment, an electrically conductive fibrous material is prepared from a thermally stabilized acrylic fibrous material by
(a) cuprous ion-impregnating the thermally stabilized acrylic fibrous material with an aqueous solution of between about 0.25 and about 10 weight percent of copper ions, added as cupric sulfate, and between about 0.5 and 10 weight percent of an hydroxylamine reducing agent while at a temperature of between about 80 and about 105.degree. C. for between about 1 and about 2 hours;
(b) subjecting the resulting cuprous ion-impregnated fibrous material to a sulfiding treatment in a solution comprising a thiosulfate sulfiding agent in a concentration of approximately 5 to 15 percent by weight while at a temperature of between about 90 and about 105.degree. C. for an additional period of time between about 1 and about 2 hours to produce an electrically conductive fibrous material having covellite copper sulfide in association therewith; and
(c) washing the resulting thermally stabilized acrylic fibrous material to substantially remove residual reactants adhering to the same.
In another aspect of the invention, an electrically conductive fibrous material is provided which comprises thermally stabilized acrylic fibrous material in association with approximately 5 to 60 percent, and preferably 35 to 60 percent, by weight of covellite copper sulfide, based upon the total weight of the product.
In another aspect of the invention, an electrically conductive composite article is prepared by a process comprising the steps of:
(a) cuprous ion-impregnating a thermally stablized acrylic fibrous material with a solution of a cupric salt and a reducing agent capable of reducing cupric ions to cuprous ions;
(b) subjecting the resulting cuprous ion-impregnated thermally stabilized fibrous material to a sulfiding treatment in a solution comprising a sulfiding agent capable of sulfiding the cuprous ions to covellite copper sulfide in association with said fibrous material to produce electrically conductive thermally stabilized acrylic fibrous material;
(c) washing the resulting electrically conductive thermally stabilized acrylic fibrous material to substantially remove residual reactants adhering to same; and
(d) incorporating the resulting electrically conductive fibrous material within a substantially continuous polymeric matrix to produce a monolithic electrically conductive composite article.
In still another aspect, a monolithic electrically conductive composite article is provided which comprises electrically conductive thermally stabilized acrylic fibrous material in association with approximately 5 to 60 percent by weight of covellite copper sulfide based upon the total weight of the conductive fiber product, incorporated within a substantially continuous polymeric matrix.
In yet another aspect, a polymer composition suitable for use in electrically conductive end uses is provided, comprising electrically conductive thermally stabilized acrylic fibrous material in association with approximately 5 to 60 weight percent of covellite copper sulfide and a polymeric carrier.